Fix deprecation notice triggered in WpOrgApi class in PHP 8.1 by wojtekn · Pull Request #5717 · wp-cli/wp-cli

Currently, the wp core download command returns a deprecated notice triggered by WpOrgApi class:

$ bin/wp core download --force
PHP Deprecated:  http_build_query(): Passing null to parameter #2 ($numeric_prefix) of type string is deprecated in /Volumes/Sites/wp-cli/php/WP_CLI/WpOrgApi.php on line 135

Deprecated: http_build_query(): Passing null to parameter #2 ($numeric_prefix) of type string is deprecated in /Volumes/Sites/wp-cli/php/WP_CLI/WpOrgApi.php on line 135

In this PR, I propose to fix the notice.